Multicolour yarn printing apparatus

ABSTRACT

A multicolour yarn printing apparatus comprising yarn transfer means for conveying groups of yarns in parallel paths printing stations spaced along the yarn groups, printing heads at each station to apply printing liquid over a predetermined length of travel of the yarn groups, each printing head comprising nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets, means for stimulating drop formation in each liquid jet, charge electrodes disposed adjacent the jets between the nozzles and the yarn groups at the location of drop formation, deflection electrodes between the charge electrodes and the yarn groups for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for collecting drops of printing liquid not needed for printing the yarns, the printing head being arranged in relation to the yarn group from below so that only deflected or, alternatively, only undeflected drops are applied to the yarns of the group.

United States Patent [1 1 Paton et al.

[ Oct. 28, 1975 4] MULTICOLOUR YARN PRINTING APPARATUS [73] Assignees: Cambridge Consultants Ltd., Cambridge, England; British Carpets Ltd., Glasgow, Scotland [22] Filed: Oct. 25, 1973 [21] Appl. No.: 409,380

[30] Foreign Application Priority Data Oct. 26, 1972 United Kingdom 49415/72 [52] US. Cl. 118/7; 118/315; 118/625; 118/630; 427/32 [51] Int. Cl. B05B 5/02 [58] Field of Search 118/7, 314, 315, 325, 420, 118/625, 624, 629, 630, 633; 117/934 R, 93.44; 28/72.6

[56] References Cited UNITED STATES PATENTS 2,883,306 4/1959 Cotter [18/325 X 3,692,466 9/1972 Mercer 28/72.6 3,714,928 2/1973 Taylor 118/624 3,717,722 2/1973 Messner 118/630 X Primary Examiner-Mervin Stein Attorney, Agent, or FirmBr owdy and Neimark [5 7] ABSTRACT A multicolour yarn printing apparatus comprising yarn transfer means for conveying groups of yarns in parallel paths printing stations spaced along the yarn groups, printing heads at each station to apply printing liquid over a predetermined length of travel of the yarn groups, each printing head comprising nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets, means for stimulating drop formation in each liquid jet, charge electrodes disposed adjacent the jets between the nozzles and the yarn groups at the location of drop formation, deflection electrodes between the charge electrodes and the yarn groups for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collectionmeans located below the yarn groups for collecting drops of printing liquid not needed for printing the yarns, the printing head being arranged in relation to the yarn group from below so that only deflected or, alternatively, only undeflected drops are applied to the yarns of the group.

15 Claims, 3 Drawing Figures U.S. Patent Oct. 28, 1975 Sheet 1 of3 3,915,113

. 1 MULTrcoLouR YARN PRINTING APPARATUS This invention relates to multicolour yarn printing apparatus for use, for example, in tufted carpet manufacture.

In a known multicolour yarn printing apparatus used in tufted carpet manufacture plain unprinted yarn is taken from a stock of reels known as the creel and transported therefrom in a large number of parallel groups of parallel yarns each containing a few yarns through printing, fixing, washing and drying stages. From the creel the groups of yarn first pass through a printing stage in which they pass between successive pairs of printing rollers on which are carried pads for applying dye to appropriate areas of each of the yarn groups. The pads are mounted each on a pin perpendicular to the face of the pad and the pin passes radially through the sidewall of the roller. A cam system inside each roller forces out the pins and pads thereon to apply the dye. Dye is taken up by the pads of the lower of each pair of two rollers which, as that roller rotates, dip into a trough of dye below the roller. Each pair of rollers thus applies only one colour and the location of the application of that colour is controlled by the cams inside the two rollers. The number of colours in a pattern is accordingly restricted to the number of pairs of rollers available. After printing the yarns pass successively through the fixing, washing and drying stages. An important limitation of the apparatus described is that in order to change the pattern printed on the yarn it is necessary to change the cam system in the pairs of rollers and this is an expensive and laborious operation. Also, it is not possible to change the length of the printed section of yarn in order to adapt the pattern for different pile heights in the finished carpet. Moreover repairs to or cleaning of a pair of rollers will generally mean that printing has to be stopped. It is an object of the invention to provide an improved multicolour yarn printing apparatus which is not subject to some, if not all, of these disadvantages.

The present invention consists of a multicolour yarn printing apparatus comprising yarn transport means for conveying in parallel paths groups of yarns each group having longitudinally extending yarns, a plurality of printing stations spaced in the direction of yarn travel, electrically operated printing heads at each station for applying printing liquid of a particular color to the respective groups of yarns in excess of the amount of printing liquid needed to print the respective groups of yarns, and, switching means for operating the printing heads so as to apply printing liquid to the corresponding yarn groups over a predetermined length of travel thereof, each printing head comprising a plurality of nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets directed towards the corresponding yarn group, means for stimulating drop formation in each liquid jet, charge electrode means disposed adjacent the jets between the nozzles and the corresponding yarn group at the location in the jets of drop formation and adapted when charged to apply charge to the drops'in the jet paths, deflection electrodes between the charge electrode means and the corresponding-yarn group for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for colle'ctingdrops of printing liquid not required for'printing the yarns, the printing head being arranged in relation to the corresponding yarn group so that only deflected or, alternatively, only undeflected drops are applied to the yarns of the group.

Advantageously, the printing heads arearranged in rows at the respective printing stations which extend transversely to the direction of yarn travel and the noz' zles of each printing head extend in a line transverse to the direction of yarn travel, the charge electrode means constituting parallel plates disposed at respective opposite sides of the jet paths from the line of nozzles.

Preferably, the deflection electrodes of the printing heads comprise parallel plates disposed respectively on opposite sides of the jet paths from the line of nozzles.

Desirably, in each row of printing heads disposed between the deflection electrodes and the yarn groups are first printing liquid collection means in the form of gut ters which extend parallel with the deflection electrodes for intercepting drops of printing liquid not required for printing while second printing liquid collection means are disposed parallel with the first printing liquid collection means below the yarn groups and serve to collect surplus printing liquid applied to the yarn groups.

Suitable means are provided for operating the switching means in accordance with a predetermined program thereby to apply color to the yarn groups in bands extending transversely with respect to the direction of yarn travel, the color of the bands being either the same or different from one to the next group of yarns.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which:

FIG. 1, is an isometric view of part of a multicolor yarn printing apparatus according to the invention for use in tufted carpet manufacture, and

FIGS. 2a and 2b are of electronic logic circuitry associated with the printing apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, multicolor yarn printing apparatus includes yarn transport mechanism (not shown) which conveys the plain unprinted yarn from the creel below electrically operated printing heads. The yarns are arranged so that they are drawn from the creel in 128 parallel groups 2 yarns each consisting of five parallel yarns, four only of which are shown. Suitably, the individual yarns in each group are spaced apart by one-eighth inches and the yarn groups have their centre lines spaced by 1% inches. After printing, the yarn groups pass through a steaming oven for fixing the dye printing liquid color in the yarns which are then washed clean of excess dye and dried before winding on beams. Here the 128 groups are separated to form five rolls of 128 yarns where each yarn on the five beams lies in the same position relatively to the yarns on the other beams of the corresponding yarn group giving five pattern repeats. The beams are suitably 18 inches long and accordingly 10 beams would be re quired for a 15 foot wide carpet.

In the multicolour yarn printing apparatus are provided, in the direction of yarn travel a succession of equally spaced printing stations 4 at each of which is located a row of printing head assemblies 6 extending transversely with respect to the yarn groups. Suitably,

the apparatus includes eight stations 4 at each of which only one colour can be printed. Each assembly 6 provides two electrically operated printing heads 8 and 10 at the location of two adjacent yarn groups 2 so that there are 1024 such printing heads.

The printing head assemblies 6 at each station 4 are supplied in groups of five from a printing liquid supply manifold 12 to which printing liquid under pressure is fed by way of an overhead pipe 14 and downpipe 16 and which supplies a nozzle plate 18 of each pair of printing heads 8 and 10. The nozzle plates are each formed with two lines of nozzles, each suitably containing twenty nozzles which lines extend above and normal and symmetrically with respect to the yarns of two corresponding groups 2. For the sake of clarity only four nozzles have been shown in each line of 20 nozzles. The nozzle plates each therefore produce two lines of 20 parallel jets of dye printing liquid directed downwardly towards the yarns of a corresponding yarn group.

It will be noted that at each station there is a row of thirteen manifolds 12 in the end manifold of which the outer end pair of heads 8 and 10 are not in use. The diameter of the nozzles is about 0.010 inches and the pressure of printing liquid in the manifolds 12 is 2 p.s.i. and adjustable to suit the viscosity of the printing liquid. The velocity of the jets which is produced is about 11.5 feet per second.

A vibration by way of a magnetostrictive vibrator paddle 20 energised from a solenoid 22 is applied to the dye liquid in each manifold 12, the solenoids 22 being powered by an amplifier using a single frequency signal from an oscillator. The vibrator paddles 20 stimulate the formation of drops in the jets from the nozzle plates, the drops in the jets being at the same frequency the oscillator signal. As the drop forming process takes a short period of time, typically 1/50th second, the jets produce drops at two to five centimeters below the nozzle plates 8. At this location the jets of each printing head 8 or 10 pass between a pair of parallel charge electrode plates 24 individual to that printing head disposed on opposite sides of and parallel with the line of jets. A voltage of about 300 volts switched by switching means (not shown) to these plates causes each jet which is electrically conductive and connected to earth via the nozzle plate 18 to take an opposite charge to that of the plate 24 and the drops breaking off from the jet retain this charge. The charged drops then fall between two deflector plates 26 one of which is earthed and the other connected to a high voltage, e.g. of 2000 volts of the opposite polarity to the voltage switched to the charge electrode plates 24. The drops and the deflector plates thus carry the same charge polarity and the drops are repelled from the deflector plate at the high voltage. Below the deflector plates and in the path of the deflected drops there extends transversely of the yarn groups and there above a dye printing liquid collection gutter 28 which connects by way of downpipes 32 with a further gutter below the yarn groups 2 the two gutters being parallel. The further gutter 30 in addition to the supply thereto of liquid deflected by deflector plates is disposed to collect surplus dye printing liquid applied to the yarn group. From the further gutters 30 the dye printing liquid is recirculated via pipes 34 and 36 to the corresponding manifold 12.

Because of the high velocity of liquid entering each gutter 28, the latter is of part cylindrical form so that liquid entering the gutter is directed round the sidewall thereof from which it drains into the bottom of the gutter and flows then by way of downpipes 32 into the associated further gutter 30.

Additional transverse gutters 31 are disposed forward, in the direction of yarn travel, of the gutters 28 and parallel with those gutters. The gutters 31 which also discharge to gutters 30 are present to catch any drops which through spurious operation such as nozzle blockage may be deflected in the direction of yarn travel.

For removing surplus droplets of printing liquid from the yarn there is provided immediately forwards of each printing station a duct 33 to which is supplied air under pressure which issues from a slot 35 in the lower wall of the duct and blows surplus liquid from the yarns into the gutter 30 therebelow.

It will be apparent that if the charge electrodes have the electrical supply thereto disconnected by the switching means the drops passing therebetween are uncharged and no deflection of the drops takes place and the undeflected drops are deposited on the yarn group therebelow, this condition prevailing until the charge electrodes are again switched to their D.C. electrical supply voltage. It will further be appreciated that at each printing station 4 the same printing colour can be applied to each of the yarn groups or, by selectively connecting charge electrodes of some of the printing heads at the particular station to their D.C. electrical supply voltage, printing by chosen printing heads is prevented.

While the apparatus described has been concerned with depositing on the yarn uncharged drops, those skilled in the art will appreciate that charged drops could be deposited and uncharged drops collected. Also it is possible to charge all drops and control the deposition of drops on the yarns by switching the field of the deflector plates on and off. In general therefore the choice is as between depositing deflected or alternatively undeflected drops and collecting the rest.

Referring now to FIGS. 2a and 2b, the pattern printed by the printing heads comprises stripes extending transversely of the yarn groups and of unit length in the direction of yarn travel, the stripes having the same or a-different color from one yarn group to the next. As there are eight colours per yarn group channel a 3-bit color code is appropriate for the electronics.

The unit length of print is well defined and affords a convenient means of encoding and storing on magnetic tape 40 of a digital tape recorder 42 the pattern information. The pattern is encoded by dividing the yarn into unit lengths, or locations, and assigning to each location one of eight colors. This is done for all 128 yarn group channels, and the 3-bit work information is prerecorded on to magnetic tape in a cyclic fashion rather than a complete channel by channel manner. By cyclic is meant the following sequence of entry printing station 1 channel 1, printing station 1 channel 2, printing station 1 channel 3, and so forth to printing station 1 channel 128, printing station 2 channel 1, printing station 2 channel 2 etc., until the end of the pattern.

During printing the data on the tape is read out, under control, at speeds in excess of 128 times the yarn transport speed. The yarn transport speed is indicated directly by the repetition rate of a pulse train CKY available on line 44. A highspeed free running multivibrator 46 having an output pulse frequency CKF at least 128 times greater than CKY is employed for reading the data from the tape 40 via a transmission gate 48 which is an AND gate having the property that when both the inputs thereto are high (the level high being hereinafter referred to as logic 1) the output goes to logic 1 whilst when either or both inputs are low (the level low being hereinafter referred to as logic 0) the output stays at logic 0. One of the inputs of gate 48 is supplied with pulse frequency CKF while the other has a control input which effects transmission or inhibition by the gate 48 of the pulse frequency.

The system of the electronics is organised so that printing is initiated by each positive going excursion of pulse frequency CKY and during a point cycle the data for the next cycle is read out from the tape 40 at high speed via buffer amplifiers 50 to 3-bit data lines 52 connected to each of the 128 logic channels the equipment serving one of those channels being contained in the area of the broken lines 54.

So as to ensure that the pattern information is read out from the tapes and multiplexed into the 128 channels during the time allocated an edge synchroniser 56 is used which is formed from two D-type latches connected in series. Upon a positive excursion of pulse frequency CKY, the negative going edge of the next pulse in pulse frequency CKF causes an output to appear at a set terminal of an S-R flip-flop latch 58 and the flipflop is actuated to provide an output which constitutes the control input to gate 48 which is enabled and the tape 40 commences and is read out one word at a time to the data lines 52 by successive CKF pulses at the output of the gate 48. Each time a word is read out by a CKF pulse to the lines 52, a data valid pulse is emitted from the recorder 42 to a counter 60 which after 128 pulses provides a pulse at its output which is supplied to the reset input of latch 58 and to a delay circuit 62. The pulse at the reset input of latch 58 causes that latch to change state and thereby disable gate 48.

The data valid pulses from the recorder 42 are also supplied to an input of a 7-bit synchronous binary counter and address generator 64 which has seven output lines connected to seven inputs of an address comparator 66 of each of the 128 logic channels. With 128 successive data valid pulses 128 coded outputs corresponding respectively to channels 1 to 128 are sequentially set up by the generator 64 and made simultaneously available to the address comparator 66 in each channel. Each comparator 66 has a fixed input code supplied to it and when the coded output from the generator 64 corresponds with the fixed input code of the comparator 66 of a particular channel, that comparator sends a pulse to the set input of an S-R flip-flop latch 68. The reset input of latch 68 is connected to the output of counter 60 so that latch 68 is reset at the end of each count of 128 data valid pulses.

When latch 68 receives an input from the associated comparator 66 the output of the latch goes from logic 0 to logic 1, the output being connected to a 3-bit parallel data latch 70 supplied from the lines 52. The change of logic level at the output of latch 68 clocks data into latch 70 but while the latch 68 has its output at logic 1 further inputs to latch 70 are ignored. Each time a word is read out of the tape 40, the channel comparators 66 sequentially supply set pulses to their respective latches 68 so that 3-bit words are sequentially clocked into the respective latches 70. When the 128 word is clocked into its channel, all the latches 68 are reset simultaneously from the output of counter 60. After a short delay the generator 64 is simultaneously reset from the output of delay circuit 62 ready to effect the next cycle of data loading into the 128 logic channels.

The data clocked into the latch 70, which it will be appreciated is a 3-bit word buffer store, appears at the output of that latch when the output of latch 68 returns from logic 1 to logic 0 during resetting. Accordingly, data appears simultaneously at the outputs of all latches from each latch 70 the data is clocked by CKY pulses supplied via lines 44 and 72 through a shift register system 74 comprising seven cascaded sections of 3-bit parallel 16-bit long shift register stages 76. At intervals of l6-bits along the shift register ie between stages 76 thereof, and at the beginning and end of the register are eight 3-bit code comparators 78. When the data clocked along the shift register by pulse frequency CKY i.e. at a rate corresponding with the yarn speed, agrees with the pre-set code of one of the comparators the corresponding printing heads or 10 as the case may be of the relevant channel is activated by disconnection of the supply potential to its charge electrode plates 24 and one of the eight colours if printed at the station 4 appropriate to that colour. The l6-bits separation between each comparator 78 corresponds to the physical spacing between printing stations.

It will be apparent that each set of 128 3-bit words are clocked through the shift registers and after every 16 steppings in the shift register the word is compared in a comparator 78 so as to activate or leave quiescent a print head at the printing station.

It will be further apparent that the overall effect of the operation of the apparatus described is that transverse bands of colour are printed on the yarn group the colour of the band at any group being one of eight different colours and the length of the bands being dictated by the requisite pile height of the carpet to be made from the yarn. It is evident that printing for carpets of different pile height is accomplished by adjustment of the length in the direction of yarn travel of the band printed.

Different pattern tapes are provided for the recorder 42 having continuous pattern repeats by either being formed in a closed loop, or by using a reversible reading machine with the pattern data appropriately ordered on the tape.

We claim:

1. Multicolor yarn printing apparatus comprising yarn transport means for conveying in parallel paths groups of yarns each group having longitudinally extending yarns, a plurality of printing stations spaced in the direction of yarn travel above the yarn groups, each printing station extending transversely of the yarn groups, electrically operated printing heads at each station for the respective groups of yarns and serving to enable printing liquid of a particular color to be applied to the groups of yarns in excess of the amount of printing liquid needed to print the respective group of yarns, and, switching means for operating the printing heads so as to apply printing liquid to the corresponding yarn groups over a predetermined length of travel thereof, each printing head comprising a plurality of nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets directed towards the corresponding yarn group, means for stimulating drop formation in each liquid jet, charge electrode means disposed adjacent the jets between the nozzles and the corresponding yarn group at the location in the jets of drop formation and adapted when charged to apply charge to the drops in the jet paths. deflection electrodes between the charge electrode means and the corresponding yarn group for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for collecting drops of printing liquid not required for printing the yarns, the printing head being arranged in relation to the corresponding yarn group so that only undeflected drops are applied to the yarns of the group.

2. Apparatus as claimed in claim 1, wherein the printing heads are arranged in rows at the respective printing stations which extend transversely to the direction of yarn travel and the nozzles of each printing head extend in a line transverse to the direction of yarn travel, the charge electrode means constituting parallel plates disposed at respective opposite sides of the jet paths from the line of nozzles.

3. Apparatus as claimed in claim 2, wherein the deflection electrodes of the printing heads comprise parallel plates disposed respectively on opposite sides of the jet paths from the line of nozzles.

4. Apparatus as claimed in claim 3, wherein in each row of printing heads disposed between the deflection electrodes and the yarn groups are further printing liquid collection means in the form of gutters which extend parallel with the deflection electrodes for intercepting drops of printing liquid not required for printmg.

5. Apparatus as claimed in claim 4, wherein downpipes are provided for discharging printing liquid from the further printing liquid collection means to the printing liquid collection means below the yarn groups.

6. Apparatus as claimed in claim 1, wherein means are provided for removing surplus printing liquid from the yarn groups.

7. Apparatus as claimed in claim 6, wherein the means for removing surplus printing liquid from the yarn groups comprise a duct extending above the yarn groups parallel with each row of printing heads and disposed forwardly in the direction of yarn travel of the row of printing heads, the duct having means for the supply thereto of air under pressure and means for directing air under pressure downwardly towards the yarn groups.

8. Apparatus as claimed in claim 1, wherein in each row of printing heads the heads are arranged in groups of successive heads, the heads of each group being supplied with printing fluid from a common manifold.

9. Apparatus as claimed in claim 8, wherein each common manifold includes means for vibrating printing fluid therein to stimulate drop formation in the printing head liquid jets.

10. Apparatus as claimed in claim 1, wherein the switching means for operating the printing heads are adapted to control the connection of an electrical supply potential to the charge electrode means.

11. Apparatus as claimed in claim 1, wherein means are provided for operating the switching means in accordance with a predetermined programme thereby to apply colour to the yarn groups in bands extending transversely with respect to the direction of yarn travel, the colour of the bands being either the same or different from one to the next group of yarns.

12. Apparatus as claimed in claim 11, wherein the programme for operating the swtiching means is formed on magnetic tape and comprises a series of multibit words representative of colours to be printed at successive yarn groups successively at the printing stations.

13. Apparatus as claimed in claim 12, wherein electronic means are provided for presenting in parallel to the printing heads at each printing station the multibit words representative of the colours to be printed and means are provided to activate the printing heads when a word representing the colour to be printed at a printing head corresponds with the colour of printing liquid supplied to that printing head.

14. Apparatus as claimed in claim 13, wherein the means for presenting in parallel to the printing heads at each printing station the multibit words include a separate shift register for each word adapted to clock the work therethrough at a speed related to yarn speed, there being connected to each shift register at spacings corresponding with the spacing of the printing stations respective preset colour code comparators whereby as a word is clocked through its shift register, when the colour of which theword is representative corresponds with the preset code of a comparator the printing head for the corresponding yarn group is activated.

l5. Multicolor yarn printing apparatus comprising barn transport means for conveying in parallel paths groups of yarns each group having longitudinally extending yarns, a plurality of printing stations spaced in the direction of yarn travel above the yarn groups, each printing station extending transversely of the yarn groups, electrically operated printing heads at each station for the respective groups of yarns and serving to enable printing liquid of a particular color to be applied to the groups of yarns in excess of the amount of printing liquid needed to print the respective group of yarns, and, switching means for operating the printing heads so as to apply printing liquid to the corresponding yarn groups over a predetermined length of travel thereof, each printing head comprising a plurality of nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets directed towards the corresponding yarn group, means for stimulating drop formation in each liquid jet, charge electrode means disposed adjacent the jets between the nozzles and the corresponding yarn group at the location in the jets of drop formation and adapted when charged to apply charge to the drops in the jet paths, deflection electrodes between the charge electrode means and the corresponding yarn group for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for collecting drops of printing liquid not required for printing the yarns, the printing head being arranged in relation to the corresponding yarn group so that only deflected drops are applied to the yarns of the group.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION d PATENT NO. 3,915,113

DATED October 28, 1975 INVENTORtS) Anthony David PATON It is certified that error appears in the ah0veidentitied patent and that said Letters Patent G are hereby corrected as shown below:

Column 2, line 37, after "are" insert --a block diagram-- Column 6, line 24, change "'if to --is-- Signed and Sealed this seventeenth Day Of February 1976 [SEAL] Arresr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofPare-nrs and Trademarks 

1. Multicolor yarn printing apparatus comprising yarn transport means for conveying in parallel paths groups of yarns each group having longitudinally extending yarns, a plurality of printing stations spaced in the direction of yarn travel above the yarn groups, each printing station extending transversely of the yarn groups, electrically operated printing heads at each station for the respective groups of yarns and serving to enable printing liquid of a particular color to be applied to the groups of yarns in excess of the amount of printing liquid needed to print the respective group of yarns, and, switching means for operating the printing heads so as to apply printing liquid to the corresponding yarn groups over a predetermined length of travel thereof, each printing head comprising a plurality of nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets directed towards the corresponding yarn group, means for stimulating drop formation in each liquid jet, charge electrode means disposed adjacent the jets between the nozzles and the corresponding yarn group at the location in the jets of drop formation and adapted when charged to apply charge to the drops in the jet paths, deflection electrodes between the charge electrode means and the corresponding yarn group for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for collecting drops of printing liquid not required for printing the yarns, the printing head being arranged in relation to the corresponding yarn group so that only undeflected drops are applied to the yarns of the group.
 2. Apparatus as claimed in claim 1, wherein the printing heads are arranged in rows at the respective printing stations which extend transversely to the direction of yarn travel and the nozzles of each printing head extenD in a line transverse to the direction of yarn travel, the charge electrode means constituting parallel plates disposed at respective opposite sides of the jet paths from the line of nozzles.
 3. Apparatus as claimed in claim 2, wherein the deflection electrodes of the printing heads comprise parallel plates disposed respectively on opposite sides of the jet paths from the line of nozzles.
 4. Apparatus as claimed in claim 3, wherein in each row of printing heads disposed between the deflection electrodes and the yarn groups are further printing liquid collection means in the form of gutters which extend parallel with the deflection electrodes for intercepting drops of printing liquid not required for printing.
 5. Apparatus as claimed in claim 4, wherein downpipes are provided for discharging printing liquid from the further printing liquid collection means to the printing liquid collection means below the yarn groups.
 6. Apparatus as claimed in claim 1, wherein means are provided for removing surplus printing liquid from the yarn groups.
 7. Apparatus as claimed in claim 6, wherein the means for removing surplus printing liquid from the yarn groups comprise a duct extending above the yarn groups parallel with each row of printing heads and disposed forwardly in the direction of yarn travel of the row of printing heads, the duct having means for the supply thereto of air under pressure and means for directing air under pressure downwardly towards the yarn groups.
 8. Apparatus as claimed in claim 1, wherein in each row of printing heads the heads are arranged in groups of successive heads, the heads of each group being supplied with printing fluid from a common manifold.
 9. Apparatus as claimed in claim 8, wherein each common manifold includes means for vibrating printing fluid therein to stimulate drop formation in the printing head liquid jets.
 10. Apparatus as claimed in claim 1, wherein the switching means for operating the printing heads are adapted to control the connection of an electrical supply potential to the charge electrode means.
 11. Apparatus as claimed in claim 1, wherein means are provided for operating the switching means in accordance with a predetermined programme thereby to apply colour to the yarn groups in bands extending transversely with respect to the direction of yarn travel, the colour of the bands being either the same or different from one to the next group of yarns.
 12. Apparatus as claimed in claim 11, wherein the programme for operating the switching means is formed on magnetic tape and comprises a series of multibit words representative of colours to be printed at successive yarn groups successively at the printing stations.
 13. Apparatus as claimed in claim 12, wherein electronic means are provided for presenting in parallel to the printing heads at each printing station the multibit words representative of the colours to be printed and means are provided to activate the printing heads when a word representing the colour to be printed at a printing head corresponds with the colour of printing liquid supplied to that printing head.
 14. Apparatus as claimed in claim 13, wherein the means for presenting in parallel to the printing heads at each printing station the multibit words include a separate shift register for each word adapted to clock the work therethrough at a speed related to yarn speed, there being connected to each shift register at spacings corresponding with the spacing of the printing stations respective preset colour code comparators whereby as a word is clocked through its shift register, when the colour of which the word is representative corresponds with the preset code of a comparator the printing head for the corresponding yarn group is activated.
 15. Multicolor yarn printing apparatus comprising harn transport means for conveying in parallel paths groups of yarns each group having longitudinally extending yarns, a plurality of printing stations spaced in the direction of yarn travel abOve the yarn groups, each printing station extending transversely of the yarn groups, electrically operated printing heads at each station for the respective groups of yarns and serving to enable printing liquid of a particular color to be applied to the groups of yarns in excess of the amount of printing liquid needed to print the respective group of yarns, and, switching means for operating the printing heads so as to apply printing liquid to the corresponding yarn groups over a predetermined length of travel thereof, each printing head comprising a plurality of nozzles, means for applying printing liquid under pressure to the nozzles to form liquid jets directed towards the corresponding yarn group, means for stimulating drop formation in each liquid jet, charge electrode means disposed adjacent the jets between the nozzles and the corresponding yarn group at the location in the jets of drop formation and adapted when charged to apply charge to the drops in the jet paths, deflection electrodes between the charge electrode means and the corresponding yarn group for deflecting charged drops in the jet paths transversely with respect to said paths and printing liquid collection means located below the yarn groups for collecting drops of printing liquid not required for printing the yarns, the printing head being arranged in relation to the corresponding yarn group so that only deflected drops are applied to the yarns of the group. 